1. Field of the Invention
The present invention relates to a cylinder block of an internal combustion engine and, more particularly, to a semi-wet liner type cylinder block in which a cylinder liner is integrally cast and a method for manufacturing such a cylinder liner.
2. Description of the Related Art
Conventionally, a wet liner type cylinder block is a known type of cylinder block for an internal combustion engine. In the wet liner type cylinder block, the cylinder liner is cooled directly by coolant in a water jacket by locating the cylinder liner so that at least a part of the cylinder liner is exposed to the water jacket. Such a wet liner type cylinder block can be manufactured by integrally casting a cylinder liner in a cylinder block body as disclosed in Japanese Laid-Open Patent Application No.5-177334.
Generally, a cylinder block body is made of an aluminum alloy in order to reduce its weight, whereas a cylinder liner is made of cast iron to provide an anti-abrasion characteristic. Since aluminum alloy has a thermal expansion coefficient greater than that of cast iron, the cylinder block body expands more than the cylinder liner when a temperature of the cylinder liner is increased due to operation of the internal combustion engine. As mentioned above, the conventional cylinder block is manufactured by integrally casting the cylinder liner in the cylinder block. Thus, when the cylinder block body expands further than the cylinder liner, it is possible that a gap is formed between the cylinder block body and the cylinder liner. Since an outer surface of the cylinder liner is exposed to the water jacket, an interface between the cylinder block body and the cylinder liner is exposed to the water jacket. Accordingly, if a gap is formed between the cylinder block body and the cylinder liner, it is possible that a coolant can intrude into the crank case via the gap.